Method for producing a fuel tank provided with internal accessories

ABSTRACT

Method for producing a fuel tank provided with internal accessories and having a wall made of plastic made in a single piece by moulding a split parison or a parison in at least two parts, said method comprising the following steps: a) the parison is introduced in the heat-softened state into a mould comprising dies; b) a core on which the accessories are placed is introduced inside the parison; c) the parison is pressed onto the dies of the mould; d) the accessories are fastened to the parison with the aid of the core in an ideal layout; e) the core is withdrawn and the mould is closed; f) the tank is moulded from the parison; and g) the tank is removed from the mould.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to French Application No. 05.06574,filed Jun. 28, 2005; French Application No. 05.08707, filed Aug. 24,2005; and French Application No. 06.01018, filed Feb. 3, 2006, theentirety of which are incorporated herein by reference.

The present invention relates to a method for producing a fuel tankprovided with (at least partly) internal accessories and in particular acomponent for putting the inside and outside of said tank into fluidcommunication.

Fuel systems on board vehicles of various types generally comprisedevices which provide ventilation of hydrocarbons contained in the tank.They may also comprise devices for supplying the engine with fuel. Suchdevices form a link between the components contained in the tank(valves, fuel pump, etc.) and components positioned outside this(canister, filling pipe, etc.). The passage through the wall of the tankmust be made taking into account the leakproof requirements laid down bycurrent environmental standards (LEV II, PZEV for example). To this end,the reduction in the number and size of openings in the wall of the tankconstitutes a favourable factor in the reduction of evaporation losses.However, this makes it more difficult to insert and position componentsinside the tank.

Moreover, the tank is generally fitted with circuits (for example forventilation, fuel supply) comprising pipes, valves, small pipes etc.positioned inside the tank and, as the case may be, connected tocomponents situated outside the tank. Now, when fluid communication ismade between the inside and outside of the tank through the wall, it ispossible, according to the position of the opening in the wall (forexample at the location of a plate), that siphons are created in thepipes. In the case of ventilation circuits, these constitute adisadvantage, since the accumulation of liquid conveyed by vapours canlead to a malfunction of the ventilation system. In addition, in thecase of fuel supply lines, it is possible that the location of the plateinvolves a detour or an unnecessary length of said pipe.

Finally, the tank generally includes other accessories such as ananti-wave (and an associated anti-noise) baffle or baffles, a device forseparating liquid from vapour, a gauge or gauges for measuring the fuellevel, a reserve tank etc. The object of the latter is to preventfailure of the pump to prime in the case where the vehicle runs out offuel or when it is parked for a long time on a slope for example. It isgenerally provided with a valve (“first fill valve”) making it possibleto fill it when the tank is first filled and/or after running out offuel, and its size is generally limited by the size of the orifice to bemade in the tank in order to be able to introduce it therein.

All these internal accessories (more exactly at least partly internalaccessories) are generally placed/attached inside the tank after this ismoulded, by separate operations that take time and labour and aretherefore costly. Moreover, as previously mentioned, with a view toreducing the size and number of orifices through the wall forintroducing said accessories, an attempt is often made to group thesetogether and, on account of this, their location is not optimal (that isto say the performance of said accessory is not optimized).

Application EP 1110697 in the name of the Applicant discloses a methodfor moulding a fuel tank using a parison in several parts so as to beable to insert the accessories into the tank at the same time as it ismoulded. With a view to reducing the number of components to beintroduced and fastened inside the tank, this document recommends theuse of pre-assembled structures, which solves the problem of the numberof openings and of the overall duration of the moulding cycle, but doesnot always solve the problem of an optimized location for the variousaccessories. The object of the invention is consequently to provide amethod which enables this problem to be solved and this by virtue of theuse of a single support (called a “core”) on which the accessories arepositioned in an ideal layout and which makes it possible to fasten saidaccessories at their ideal location in the tank in a single step. Inparticular, in a variant, the method according to the invention makes itpossible to produce a fuel tank made of plastic with fluid communicationbetween the inside and outside of said tank, through an opening withreduced dimensions, the location of which may be freely chosen so as toprevent the creation of siphons and/or detours of the lines and this bymeans of a method involving a minimum number of steps.

To this end, the invention relates to a method for producing a fuel tankprovided with internal accessories and having a wall made of plasticmade in a single piece by moulding a split parison or a parison in atleast two parts, said method comprising the following steps:

-   a) the parison is introduced in the heat-softened state into a mould    comprising dies;-   b) a core on which the accessories are placed is introduced inside    the parison;-   c) the parison is pressed onto the dies of the mould;-   d) the accessories are fastened to the parison with the aid of the    core in an ideal layout;-   e) the core is withdrawn and the mould is closed;-   f) the tank is moulded from the parison; and-   g) the tank is removed from the mould.

“Accessory” is understood to denote, within the context of theinvention, a component or assembly of components having an activefunction in the tank such as to ventilate, to convey fuel to the engine,to measure the liquid level, to reduce noise associated with waves etc.In particular, it consists of a component or assembly of components ofwhich the function may be optimized according to its or their location.In particular, it may consist of a ventilation line and/or a line forsupplying fuel or electricity, the location of the outlet point of whichcan consequently be freely chosen (in order to prevent the formation ofsiphons and/or to enable the length of said line to be optimized and/orto increase the working volume of the tank). Similarly, it may consistof an anti-slosh baffle or baffles of which the acoustic performancedepends in particular on the position of the fuel gauge or gauges, themeasuring precision of which also depends on the position. The inventionapplies particularly well to components establishing fluid communicationbetween the inside and outside of the tank, such as the aforementionedventilation and fuel supply lines, since it also enables, according toone of its variants, a completely leakproof fluid communication to beobtained.

According to this variant, during step b), there is introduced insidethe parison at least part of a component comprising a pipe and/or anorifice for the passage of fluid and, during step d), this componentpart is fastened to the parison, the method according to this variant ofthe invention additionally comprising a step during which an opening ismade in the wall of the tank, this opening being localized at the placewhere the component part is fastened to the parison so as to free theopening or pipe therefrom and to permit fluid communication between theinside and outside of the tank.

A fuel tank is understood to mean a leakproof tank capable of storingfuel under the conditions of use and under diverse and variousenvironmental conditions. An example of this tank is one which is fittedto motor vehicles.

The fuel tank according to the invention is made with a plastic wall,generally comprising an inner face on its concave part and an outer faceon its convex part.

Plastic denotes any material comprising at least one polymer made ofsynthetic resin.

All types of plastic are suitable. Plastics that are particularlysuitable belong to the category of thermoplastic materials.

A thermoplastic material denotes any thermoplastic polymer includingthermoplastic elastomers, as well as mixtures thereof. The term“polymer” denotes homopolymers as well as copolymers (in particularbinary or ternary). Examples of such copolymers are, in a non-limitingmanner: copolymers with a random distribution, sequenced copolymers,block copolymers and grafted copolymers.

Any type of thermoplastic polymer or copolymer of which the meltingpoint is below the decomposition temperature are suitable. Syntheticthermoplastic materials which have a melting range extending over atleast 10 degrees Celsius are particularly suitable. As an example ofsuch materials, are those that have a polydispersion of their molecularweight.

In particular, use may be made of polyolefins, thermoplastic polyesters,polyketones, polyamides and copolymers thereof. A mixture of polymers orcopolymers may also be used, as well as a mixture of polymeric materialswith inorganic, organic and/or natural fillers such as, for example, ina non-limiting manner: carbon, salts and other inorganic derivatives,natural or polymeric fibres. It is also possible to use multilayerstructures consisting of stacked cohesive layers comprising at least oneof the polymers or copolymers described above.

A polymer that is often employed is polyethylene. Excellent results havebeen obtained with high density polyethylene (HDPE).

Preferably, the tank for which the method according to the invention isintended, comprises a multilayer structure comprising at least one layerof thermoplastic material and at least one supplementary layer whichcan, advantageously, consist of a material that is a barrier to liquidsand/or gases.

Preferably, the nature and thickness of the barrier layer are chosen soas to limit to the maximum the permeability to liquids and gases incontact with the wall of the tank. Preferably, this layer is based on abarrier material, that is to say a resin that is impervious to fuel suchas EVOH for example (partially hydrolysed ethylene-vinyl acetatecopolymer). Alternatively, the tank may be subjected to a surfacetreatment (fluorination or sulphonation) aimed at making it imperviousto fuel.

A parison, is understood to mean a preform, generally extruded and withany shape, generally substantially flat or tubular which is intended toconstitute the wall of the tank after moulding, that is to say after anoperation which consists of giving the parison which is in theheat-softened state, the required shapes and dimensions with the aid ofa mould so as to obtain a tank in one piece.

The method according to the invention uses a core. This is understood tomean a part of a suitable size and form so as to be capable of beinginserted between the cavities of the mould. Such a part is for exampledescribed in patent GB 1, 410, 215, of which the contents are introducedto this end as a reference in the present application. Within thecontext of the invention, the main function of the core is to positionand fasten accessories onto the parison. When the accessories arefastened by welding, the core may be provided with heating parts(mirrors for example) keeping hot the part of the accessory to be welded(which is generally preheated, by infrared heating for example, besidethe core). It may be provided with heating parts (filaments for example)in the zone or zones that will be in contact with the parison during theplacement of accessories (see further on).

It should be noted that preheating the components within the context offastening a component by welding, should not be compulsorily made ontothe core. Mirrors (or other preheating tools) may be positioned forexample on the frame of the machine without forming part of the core. Onthe other hand the mirror (or other preheating tool) should bepositioned at the right moment in the cycle at the right location inorder to be able to preheat the component.

The core may also serve to blow in gas under pressure into the mould inorder to press the parison onto the dies of the mould. In this way itcontributes to moulding the tank, even providing the major part of thedeformation of the parison (typically of the order of 80%, or even 90%and even at least 95% of the deformation required to obtain the tank)before the accessories are fastened there.

To this end, the core possesses at least one orifice connecting theinner space of the core to a 3-way valve, connected on the one hand toan external source of air under pressure and, on the other hand,directly connected to atmosphere. During the first blow moulding, thecontrolled 3-way valve connects the air reservoir to the core in thisway releasing air in the core and the mould. At the end of this firstblow moulding, before opening the mould, the core must be connected tothe atmosphere, which is carried out by controlling the 3-way valve,this time connecting the volume of air of the core with the outside. Analternative design consists of making two orifices in the core, with twoseparately controlled 2-way valves, one connected to the air reservoirand the other to the atmosphere.

Air is injected into the core via a single orifice, calculated for agiven flow rate (ideally with a diameter of two inches) or via a holeprovided with a blow moulding nozzle. The nozzle then enables the airjet to be directed, and in this way to prevent any impact of the airflowonto a heating element or a component to be installed in the tank.

The circuit for pre-blow moulding (or for blow moulding into the core)described above is completely independent of the inflation circuit whichensures the second blow moulding.

Finally, the core may also be used to control the method, at least inpart. To this end, a camera can be incorporated for example at the coreso as to visualize and check, by image analysis, the quality of theattachment of accessories. One or more sensors for measuring values suchas force, travel, pressure and temperature can also be installed on thecore so as check more effectively the attachment of accessories.

In the method according to the invention, the internal accessories arefastened onto the parison with the aid of the core according to an ideallayout. This is understood to mean that at least some of these have alocation such that their performance is optimized. Preferably, thislayout is such that, overall, the performance of the tank and/or itsworking internal volume are optimized. In order to enable the core toperform such positioning, it is advantageous to pre-position theaccessories at the corresponding location on the die before the diescarrying the parison surround the core carrying the accessories. Inother words, they are pre-positioned on the core so as to be as near aspossible to the corresponding ideal location on the dies when the mouldis closed.

It may also be advantageous to provide the core with one or more jacksenabling the component to be firmly fastened by welding or pop-riveting.

In the method according to the invention, the tank is moulded in asingle piece (in a single step following which a tank is obtained in asingle piece, without recourse to a supplementary step of assemblingseparate shells) from a spilt parison or a parison in at least twoparts, and this generally by welding the slit or the two parts of theparison when the mould is closed. In particular, advantageously, thetank is moulded by:

-   -   blow moulding, that is to say by expanding and pressing a        tubular parison comprising at least one cut-out onto the walls        of a mould by means of a pressurized fluid (as described in        application EP 1110697, the contents of which are incorporated        to this end by way of reference in the present application);    -   thermoforming sheets, that is to say by pressing these against        the walls of a mould, for example by creating suction (making a        vacuum) behind these.

In the method according to the invention, the so-called forming of theparison (that is to say its deformation in order substantially toacquire the shape of the tank) principally takes place during step c).During step f) (during which the abovementioned welding is carried out)pressure (or suction) is simply maintained so as to ensure thedimensional stability of the tank.

In the case of a blow moulded tank, after extrusion of a single tubularparison, the latter is cut over all or part of its length, preferablyalong two diametrically opposed lines.

Compared with the blow moulding of two extruded sheets separately, andof which the thickness is constant, this way of proceeding makes itpossible to use parisons with a variable thickness (that is to say notconstant over the length), obtained by means of a suitable extrusiondevice (generally an extruder provided with a die with a plunger ofwhich the position is adjustable). Such a parison takes account of thereduction in thickness which takes place during blow moulding at someplaces of the parison, following an irregular degree of deformation ofthe material in the mould.

Preferably, the tank is moulded by blow moulding. In point of fact,thermoforming generally involves heating the mould to 60° C. so as to beable to achieve deep deformations (corners of the tank for example wherethe parison is highly stretched). The result is cycle times that arelonger than with blow moulding, where this constraint does not exist.

To this end, the dies of the mould are generally closed on the core—thatis to say they are in contact with it and delimit a sealed zone eitherside of the core—during steps c) and d). Or more exactly: since thesedies carry the parison, the core is in contact with the parison, whichis consequently held in a sandwich between the core and the dies of themould. This contact zone is preferably outside the weld zone. If thecontact zone with the core comprises/is the weld zone of the parison, itis then preferable to heat the core in the contact zone so as to ensurewelding. It then consists to some extent of a first closure of themould, with the core inserted between and in contact with the dies, andby which pressurized gas (generally air), is blow in. Generally, thiszone is located in the peripheral part of the dies and often is also inthe peripheral part of the core. This first closure of the mouldconstitutes what is called “pre-blow moulding” (or first blow moulding).

The pressure of the gas during the pre-blow moulding step is preferablygreater than or equal to 1 bar, preferably 2 bar, or even 3 bar. It ishowever generally below or equal to 6 bar, preferably 5 bar.

The pressure of the gas for blow moulding after the second closure ofthe mould is generally higher, typically greater than 6 bar, preferably7 bar. It advantageously however does not exceed 10 bar.

During the blow moulding steps, the pressure of the gas advantageouslycombines with a pressure reduction (application of vacuum) behind thedies (or outer parts) of the mould. This pressure reduction ispreferably of the order of hundreds of mbar (typically between 100 and500 mbar, preferably between 200 and 400 mbar).

In the case of moulding by blow moulding, the method according to theinvention also includes a degassing step which is carried out beforeeach opening of the mould, that is to say before steps e) and g).

The degassing step may be carried out in a suitable manner. Generally,the parison is first of all pierced (for example by pricking it with aneedle) and then the fluid is evacuated from the mould (for example withthe aid of a valve). In the case where the tank is moulded bythermoforming, it is not necessary for the mould to be closed onto thecore in order to press the latter onto the dies (since pressing is doneby suction under the latter and not by blow moulding via the core).

In this variant of the invention (where the tank is moulded by blowmoulding carried out at least partly by the core), it is advantageousfor pre-blow moulding with the aid of the core to be such that theparison already substantially has the dimensions of the tank (or inother words, the deformation of the parison takes place substantiallyduring this step and not during the second closure of the mould).

During the method according to the invention, there is preferably adevice preventing the slit or edges of the parts of the parison fromwelding during the first closure of the mould (when the parison ispressed onto the dies so as to fasten the accessories onto the parison).This device is advantageously incorporated in the core. To this end, thecore preferably has a suitable shape and size so as to be partly(generally at least over part of its periphery) inserted between theparts of the parison to be welded (lips of the slit or edges of the twoparts). In order to facilitate welding during step f), the dies of themould are advantageously provided with a thermal regulation deviceenabling the weld zone to be heated during the steps concerned by thefirst closure of the mould, where appropriate.

As mentioned previously, the core may also incorporate such a device(for thermal regulation) in its contact zone or zones with the parisonand this in particular in the case where this includes theaforementioned weld zone. This variant could improve still further thequality of the weld of the tank (by reducing the internal bead andtherefore by improving the impact resistance of the tank). Such anapparatus is for example described in application FR 04.13407 in thename of the Applicant, the contents of which are incorporated to thisend by reference in the present application.

According to a first preferred variant, the accessories that arefastened onto the parison with the aid of the core comprise a reservetank making it possible to prevent a failure of the pump to prime in thecase where there is a breakdown due to lack of fuel or during parkingfor a long time on a slope for example. Recourse to the method accordingto the invention makes it possible not only freely to choose the volumeof this tank (and therefore by choosing a large size for this to satisfythe specifications of all car manufacturers), but also to optimize theposition of the latter so that it can be connected directly to thefilling pipe (optionally via a leakproof flexible connector (made ofrubber and/or corrugated)) so as to avoid having recourse to a “firstfill valve” as previously explained. In this variant, the non-returnvalve (ICV) generally present at the bottom of the filling pipe mayadvantageously be incorporated in the abovementioned flexible connector,and this for reasons of ease of assembly.

The tank according to this variant of the invention may be fastened tothe parison by any suitable means (welding, overmoulding, pop-rivetingetc). The technique of pop-riveting is particularly well suited.

According to another preferred variant already previously mentioned, atleast one accessory comprises a component provided with a pipe or anopening for the passage of a fluid. The component referred to in thisvariant of the invention is an object which permits fluid (vapour and/orliquid) communication between the inside and outside of the fuel tank.It may consist of a small pipe, a valve etc. It advantageously consistsof at least one part of the ventilation line or of the fuel supply lineof the tank.

This object preferably comprises a base, generally in a flattened form,and at least one profiled part or pipe. The base generally has aperimeter with a circular shape and the pipe generally has asubstantially cylindrical shape. In a preferred manner, this pipe issituated at least partly outside the tank when the component is fastenedto the wall of the tank. It enables a connection to be made to acanister for example, in the case where the component serves to attach aventilation circuit. It may also enable a connection to be made to theengine, in the case where the component serves to attach the line forconveying fuel to the engine. It should be noted that the component mayinclude a second pipe for internally connecting the ventilation line orthe fuel line coming from the pump. In this case, advantageously, saidinternal lines are connected to the component before it is fastened tothe wall, while the external lines are attached afterwards to themoulded and preferably set (cooled) tank.

By establishing fluid communication between the inside and outside ofthe tank, the component is generally a network of an assembly ofelements that communicate with each other.

The component may be made of any material with suitable mechanicalstrength and suitable resistance to chemicals (to fuels). It ispreferably made of metal or plastic. Plastics are preferred for theirlightness and ease of application. Any type of plastic may be suitable.Preferably, a plastic is chosen of which the dimensional stability isgood in a medium subjected to temperature variations of the order ofseveral tens of degrees Celsius. A plastic is also preferably chosen ofwhich the dimensional stability is unaffected by contact with liquidsand gases likely to be contained in the tank, and which is impermeable.Polyacetals, polyamides, polyesters and polyvinyl halides give goodresults. Plastics which are well suited, are polyacetals and inparticular POM (or polyoxymethylene). In a particularly preferredmanner, the component is made of injected plastic, that is to say havingbeen formed by an injection moulding technique under pressure in amould.

The component may be based on a material having low permeability tofuels or made of polyethylene. Preferably, when the component is basedon polyethylene, it is treated so as to reduce its permeability. Thetreatment consists for example of sulphonation or fluorination of thecomponent.

According to this variant of the invention, at least one part of thecomponent of the parison is attached during production of the tank bymoulding, that is to say before the mould is closed in step e).

Part of the component is secured to the parison by any suitable means.Generally, it involves the use of a support. A support is understood todenote a movable part capable of being secured temporarily to thecomponent part so that it can be introduced into the parison and is ableto be attached there (secured to the internal wall thereof).Conventional blow moulding methods often use a blow moulding blowpipedesigned to introduce pressurized fluid which serves to blow into themould, inside the parison. This blowpipe can serve as a support.Alternatively, a robot arm can be used as a support. This solution isquite suitable in the case of moulding by thermoforming. Finally, inmoulding methods that make use of a core, the latter may act as asupport.

By virtue of the movable nature of the support (core), the component ispositioned inside the parison and, as soon as the correct position ofthe component is achieved, the component is fastened to the parison (toa portion of the internal surface thereof). Any fastening techniqueknown to a person skilled in the art may be used within the context ofthe invention. It is possible for example to fasten, with the aid of thecore, the component to the parison by pop-riveting or by welding thematerial in the contact zone of the component with the parison. It isalso possible to overmould at least part of the component with the aidof the parison and/or to weld the component onto the said parison (inthe case of compatible materials).

Once the component has been fastened to the parison, the support iswithdrawn from the mould, where appropriate, and the mould is thenclosed onto the parison in order to produce the tank.

The method according to this variant of the invention additionallyincludes a step during which an opening is made in the wall of the tankand which can form part of the moulding method or be subsequent thereto.When the opening is made during moulding, it is preferably made bypiercing the parison by means of a needle while the parison is put underpressure. In this case, movement of the needle is liable to create aspur of material on the periphery of the opening and this spur willadvantageously be removed after the tank is moulded.

Consequently, in a preferred manner, the opening is made after the tankhas been moulded, for example by cutting out a portion of the surface ofthe wall of the tank.

According to this variant of the invention, the component may compriseone or more assembled parts.

According to a first variant, the component consists of a single piececomprising a pipe and that this piece is fastened so that it passesthrough the opening in the wall of the tank. This variant has thedisadvantage that an opening in the wall of the tank has to be made asthe tank is moulded, before said component is fastened to the parison inorder to allow the pipe to pass through the wall. Now, in this case, theparison is malleable and the shape of said opening is not then perfectand may require subsequent machining on the finished (cooled) tank.

According to a second variant, that is preferred (since it permits theproduction of the opening after the tank is moulded), the componentcomprises at least two parts, each provided with a pipe or orifice andfollowing step f) the second part is fastened to the first or to theperiphery of the opening in the wall of the tank outside this so thatthe pipes/orifices of these parts allow fluid to pass between the insideand outside of the tank. It is possible for example to attach the secondpart to the wall of the tank by welding onto the outer face thereof, onthe periphery of said opening. Alternatively, the two parts could beprovided with means of assembly capable of cooperating together in orderto attach the second part onto the first.

In the method according to this variant of the invention, the componentallows fluid communication between the inside and outside of the tank ina generally leakproof manner through the opening made in the wall of thetank.

Leakproofness is understood to be in relation to the liquid and/or gascontained in the tank under normal temperature and pressure conditionsof use for the tank.

This leakproofness to liquids and gases is preferably ensured by thepresence of a compressible seal inserted between one surface of thecomponent and the wall of the tank. The seal used may have severalshapes. It may for example consist of an o-ring. An o-ring with acircular cross section has given good results.

The compressible seal is generally made of an elastomeric plastic or ofrubber. Preferably, the material of the seal is chosen to be a materialthat is inert to liquids and gases in contact with the concave surfaceof the tank.

The seal is preferably inserted in a groove so as to be compressed whenthe component is secured to the wall of the tank.

The component is advantageously positioned so that the o-ring is incontact with a barrier layer of the tank when the latter has a wall witha multilayer structure.

A special situation is envisaged when it is desired to attach to theparison a component such as a small pipe connected to an internalventilation circuit, generally comprising a valve or several valves aswell as a tank for separating liquid from vapour (so as to prevent dropsof liquid fuel from being entrained to the canister, such a device beingindispensable if the zero emission standards for vehicles (“ZEV” in theUnited States) are to be complied with). Starting from the steps of themethod described above, the small pipe (and the ventilation circuitprovided with its valves and its tank, where appropriate) is first ofall attached to the core. Next, the core carrying the small pipe isintroduced into the parison and the mould is closed. The parison ispressed onto the dies of the mould by blowing through the core and/or bysuction under vacuum behind the dies.

During this step, there is equilibrium between the pressures inside theparison and inside the ventilation circuit, the pressure being equal tothe blow moulding pressure. The small pipe is then attached to theparison with the aid of the core, and the mould is then degassed andopened in order to withdraw the core. At this stage, the pressure insidethe parison is equal to atmospheric pressure while the pressure insidethe ventilation circuit remains at the blow moulding pressure. In pointof fact, since the parison is generally oriented along a substantiallyvertical axis, the valves are oriented along a substantially transverseaxis with respect to that of the parison, that is to say atapproximately 90° with respect to the vertical.

In this situation the valves are generally closed, the blow mouldingfluid being partly trapped inside the ventilation circuit. Since theventilation circuit is not generally perfectly leakproof, the pressureinside said circuit tends towards atmospheric pressure since, in spiteof their orientation, the valves have the tendency to open on account oftheir geometry and on account of the positive pressure differencebetween the inside of the ventilation circuit and the pressure insidethe parison.

The mould is then closed in order to blow in a fluid under pressure. Atthis time, the pressure inside the ventilation circuit remains at theatmospheric pressure level without being brought again into equilibriumwith the blow moulding pressure, since the valves are once again closed,this time because a negative pressure difference exists between theinside and outside of the ventilation circuit. As the method accordingto the invention proceeds, the ventilation system is generally subjectedto a high pressure (equal to the blow moulding pressure, that is forexample 10 bar) and this may lead to a deterioration in the valves. Inorder to remedy this disadvantage, equilibrium of pressure between theventilation circuit and the internal pressure of the tank isadvantageously provided by making an orifice in the small pipe attachedto the wall of the tank. Said orifice will be closed after the blowmoulding phases.

It should finally be noted that within the context of the invention, itmay be advantageous to provide the core with “forms” (or forming tools)having an adjustable temperature and of which the aim is to assist inimproving the distribution of thicknesses. As soon as the mould isclosed for the first time on the core (in order to attach theaccessories) jacks could move these forms and accompany the forming andstretching of the material (in order to improve the distribution ofthicknesses).

FIGS. 1 to 3 aim to illustrate some concrete aspects of the invention,without in any way restricting its scope.

FIG. 1 represents a component in two parts (2, 3), one of which (2) iswelded onto the inner face of the wall (1) of a fuel tank and the other(3) is welded onto its outer surface. The two parts (2, 3) rest on theperiphery of an opening made in the wall (1) of the tank.

FIG. 2 represents a component in one piece (2) welded onto the innerface of the wall (1) of a tank and of which a part (with a tubularshape) passes through an opening made in the wall (1) of the fuel tank.Since the component is in a single piece and comprises a pipe which mustpass through the wall (1) of the tank, the orifice in this wall has tobe made before said component is fastened to the parison when the latteris moulded. The presence of two spurs (1′) will consequently be observedcreated by the movement of the needle that has been used to make theopening in the wall of the tank during moulding. These spurs (1′) areremoved during a finishing step.

FIG. 3 corresponds to an embodiment where a component comprises a part(2) welded onto the inner face of the wall (1) of the tank and providedwith means of assembly. These means of assembly cooperate with the meansof assembly of a second part of the component (3), partly inside thetank. The part (3) includes an o-ring (5) which is in contact with abather layer (4) included within the multilayer structure of the wall(1).

The invention claimed is:
 1. A method for producing a fuel tank providedwith internal accessories and having a wall made of plastic made in asingle piece by moulding a split parison or a parison in at least twoparts, said method comprising the following: a) the parison isintroduced in the heat-softened state into a mould comprising dies; b) acore on which the accessories are placed is introduced inside theparison; c) the mould is closed and the parison is pressed onto the diesof the closed mould, such that the dies carry the parison and the coreis in contact with the parison, and the parison is held in a sandwichbetween the core and the dies of the mould; d) the accessories arefastened to the parison with the aid of the core in a predeterminedlayout and the mould is opened; e) the core is withdrawn from the openedmould and the mould is closed; f) the tank is moulded from the parisonin the closed mould; and g) the mould is opened and the tank is removedfrom the opened mould.
 2. The method according to claim 1, wherein atleast one accessory is selected from the group consisting of aventilation line, a line supplying fuel or electricity, one or moreanti-wave baffles, a reserve tank and a fuel gauge.
 3. The methodaccording to claim 1, wherein a camera and/or at least one sensor formeasuring values such as force, travel, pressure and temperature isincorporated in the core.
 4. The method according to claim 1, wherein atleast one accessory comprises a component provided with a pipe and/or anorifice for the passage of fluid and according to which during b), thereis introduced inside the parison at least part of the component and,during d), this component part is fastened to the parison, this methodadditionally comprising making an opening in the wall of the tank, thisopening being localized at the place where the component part isfastened to the parison so as to free the opening or pipe therefrom andto permit fluid communication between the inside and outside of thetank.
 5. The method according to claim 4, wherein the component consistsof a single piece comprising a pipe and that the pipe is fastened sothat it passes through the opening in the wall of the tank.
 6. Themethod according to claim 4, wherein the component comprises at leasttwo parts, each provided with a pipe or orifice and that following f)the second part is attached to the first part or to the periphery of theopening in the wall of the tank outside this so that the pipes/orificesof the parts allow fluid to pass between the inside and outside of thetank.
 7. The method according to claim 6, wherein the second part isfastened to the wall of the tank by welding onto the outer face thereof,on the periphery of said opening.
 8. The method according to claim 6,wherein each of the two component parts includes a means of assembly,and wherein the second part is positioned on the first part so that eachof said means of assembly cooperate together.
 9. The method according toclaim 1, wherein the tank comprises a multilayer structure, themultilayer structure comprising at least one thermoplastic layer and atleast one barrier layer.
 10. The method according to claim 9, wherein atleast one accessory comprises a component provided with a pipe and/or anorifice for the passage of fluid, and the component comprises an o-ringwherein the component is positioned so that said o-ring is in contactwith the barrier layer of the tank.
 11. The method according to claim10, wherein the component comprises polyethylene and has been subjectedto a surface treatment or comprises a material having low permeabilityto fuels.
 12. The method according to claim 1, wherein the accessoriescomprise an internal ventilation circuit provided with at least onevalve and a small pipe, wherein the tank is moulded by blow moulding andthe small pipe has an orifice that is closed after the tank is blowmoulded.
 13. The method according to claim 1, wherein the accessoriescomprise a reserve tank, and the reserve tank is positioned to beconnected directly with a pipe for filling the tank.
 14. The methodaccording to claim 13, wherein the connection between the reserve tankand the filling pipe comprises a flexible connection incorporating anon-return valve.
 15. The method according to claim 13, wherein thereserve tank is fastened to the parison by pop-riveting.
 16. The methodaccording to claim 1, wherein the core comprises at least one formhaving an adjustable temperature and being actuated by a jack so as toaccompany the forming and stretching of the plastic.
 17. The methodaccording to claim 6, wherein each of the two component parts comprisesan assembly member, and wherein the second part is positioned on thefirst part so that each of said assembly members cooperate together.